Data mirroring is a good start for moving to a 24/7 environment. For mainframe DB2 there are several options for mirroring. Of course, IBM offers options for mirroring data, but you ask about non-IBM tools. Two software companies that sell mirroring solutions are Mainstar Solutions (www.mainstar.com) and Data Mirror (www.datamirror.com). I have no experience with either nor do I know their specific capabilities. So I suggest that you investigate the solutions they offer.
Another option is to look at disk storage hardware that provides mirroring capabilities. IBM, Hitachi, and others offer hardware mirroring options.
This was first published in May 2003